Butter a 9×5-inch loaf pan and add a parchment paper sling.
In a large bowl, melt the butter, then whisk in the brown sugar until smooth, then whisk in the mashed bananas and eggs. Stir in the remaining ingredients, giving them a stir and a whisk a few times to make sure they are all incorporated into the batter and no dry pockets remain. Transfer the batter to the loaf pan and smooth the top. Sprinkle the top of the loaf with about 1 teaspoon of cinnamon and 2 teaspoons of sugar if you wish.
Preheat the oven to 350℉. Let the batter rest while the oven heats. Place the bread in the oven and bake for about 50-60 minutes, until a tester comes out clean. Cool in the pan, then turn out to cool completely on a rack before cutting.